Conventionally known disposable diapers include disposable diapers that include a front abdominal section disposed on the abdomen of the wearer, a rear dorsal section disposed on the buttocks of the wearer, and a crotch section that extends from the front abdominal section, passing between the legs of the wearer, up to the rear dorsal section.
In this disposable diaper, both side edges of the front abdominal section and both side edges rear dorsal section are welded to each other in such a manner that the front abdominal section and the rear dorsal section are connected in the form of a ring.
To produce a disposable diaper of this type, there is firstly prepared a continuous body in which constituent elements each constituted by connecting the front abdominal section and the rear dorsal section via the crotch section in the longitudinal direction are continuous in a transversal direction.
The continuous body is then folded in half in the longitudinal direction; in this state, an overlap portion of the front abdominal section and the rear dorsal section is ultrasonically welded, and the continuous body is cut in the transversal direction in such a manner that the resulting weld portions are present on both sides of the crotch section.
An ultrasonic horn that applies ultrasonic vibration to the continuous body having been folded in half is used herein for ultrasonic welding (see, for instance, Japanese Patent No. 4592690).
The continuous body includes a nonwoven fabric sheet, a waterproof sheet and an elastic body, and the thickness dimension of the overlap portion of the continuous body is large and uneven.
Accordingly, there is a demand for larger amplitudes (hereafter, output amplitude) of the ultrasonic vibration that is output by the ultrasonic horn, in order to generate effectively thermal energy, through ultrasonic vibration, in such an object to be welded.